An optical lens refers to an object which is made of a transparent material in order to collect or distribute light. The optical lens may be produced by a method of forming a desired shape by polishing an object made of a transparent material (e.g., glass or crystal).
Recently, an optical lens production method has been introduced, which produces an optical lens by melting a polymeric compound such as plastic and injecting the polymeric compound into a mould. In the case of the plastic injection molding method, a cavity, which is formed to correspond to a shape of a desired lens, is present in the mould, and an injection machine injects a molten plastic resin into the mould through a sprue. The injected molten plastic resin is received in the cavity in the mould, and then cooled. After the plastic is completely cooled, the plastic has a shape corresponding to the shape of the cavity, such that the optical lens is produced.
In the case of the optical lens production method using the plastic injection molding, a birefringence phenomenon may occur in the plastic, which defines the optical lens, because of a difference in cooling speed of the molten plastic resin. To reduce the birefringence phenomenon caused by a difference in cooling speed of the plastic resin, injection pressure of resin may be increased, or a temperature of the mould may be kept high, but this method decreases a production speed, and thus degrades productivity.
Meanwhile, a photocurable resin refers to a synthetic organic material which is cross-linked and cured by receiving light energy such as ultraviolet (UV) rays or electron beams (EB). The resin, which is curable by an ultraviolet ray, is called an ultraviolet ray curable resin, and the resin, which is curable by an electron beam, is called an electron beam curable resin. As an alternative to the optical lens production method using the injection molding of the plastic resin, a method of producing an optical lens using a photocurable resin has been developed. Korean Patent Application Laid-Open No. 10-2010-0088480 discloses a method of producing an optical lens using an ultraviolet ray curable resin.
In a case in which the optical lens is produced by using the photocurable resin, there is a need for a production method which efficiently produces the optical lens and obtains a high yield.